Krebs cycle or tricarboxylic acid (TCA) cycle or citric acid cycle is the pathway where pyruvate is converted to CO2and intermediates are used for oxidative phosphorylation. Before pyruvate that has been generated can enter the Krebs cycle, pyruvate is first decarboxylated, leading to the production of CO2, NADH, and the energy rich acetyl-CoA. The cycle begins with the combination of the acetyl group of acetyl-CoA with the four-carbon compound oxaloacetate to form a six-carbon citric acid compound. During the cycle, two additional CO2分子,更多的NADH和FADH形成。在the end, oxaloacetate is regenerated to return as an acetyl acceptor, and the cycle is completed.